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1994 E500 changed spark plugs, now runs rough, bad spark plug wire

I just changed out the spark plugs with Mercedes Benz spark plugs sourced from Gerry (thank you). Unfortunately car didn't run right after I changed the plugs. Looking at my extensive maintenance records I see no evidence of ignition wire change. Other photos on this site confirm I am still on the original ignition wires. Spark plugs were last changed at 91,000 miles in 2001 (146,000 on car now).

Hmm... I wonder what the problem is? I think handling my original wires send #1 over the edge. I just ordered a new Bosch spark plug wire set and hopefully that will cure the problem. Rotors and Caps were changed 9 months ago at 142,000 miles by previous owner but they didn't bother with the wires.

Anybody have a tip on how to remove and replace the wire going to the coil that appears to be under the ABS control pump? That is one tight fit.

Anybody have a tip on how to remove and replace the wire going to the coil that appears to be under the ABS control pump? That is one tight fit.

It will be easier if you remove the headlight for access to the coils. Note that aftermarket wires may have non-factory lengths, and you may need to experiment to get the appropriate wire to each cylinder. The wire tray has numbers in the bottom (use flashlight) that show which wire goes in which slot, and which is on top/bottom in the tray.

Guys, thanks so much, hope I don't end up cursing the Bosch wire set I ordered in terms of lengths. BTW, is their a recommended set to order the works right every time? I ordered my set from Pelican Parts.

I just changed out the spark plugs with Mercedes Benz spark plugs sourced from Gerry (thank you). Unfortunately car didn't run right after I changed the plugs. Looking at my extensive maintenance records I see no evidence of ignition wire change. Other photos on this site confirm I am still on the original ignition wires. Spark plugs were last changed at 91,000 miles in 2001 (146,000 on car now).

Hmm... I wonder what the problem is? I think handling my original wires send #1 over the edge. I just ordered a new Bosch spark plug wire set and hopefully that will cure the problem. Rotors and Caps were changed 9 months ago at 142,000 miles by previous owner but they didn't bother with the wires.

Anybody have a tip on how to remove and replace the wire going to the coil that appears to be under the ABS control pump? That is one tight fit.

I know it is kind of an old post.....But having a little issue with my RPM in cold start ( fluctuates a little until it settle down )....
I might have to replace my wires : my question : HOW to do test the wire resistance?? Do you remove them completely, or just the boot going to the spark plug.
Could anyone let me know the exact procedure?
Thank you in advance.

There is no exact way that is correct. You use the ohm setting on your multi meter.

I would personally, go from the contact inside the distributor cap to the plug connector. If you have a bad resistor end- they are replaceable.. IE you don't have to buy a new set of wires. The wires them selves are copper core and silicone insulation.

I would also check the resistance of the dist rotor from center to outside edge. I think they are marked or in the FSM.. I've seen some crazy high readings on them... a little cleaning and it comes down to normal.

There is no exact way that is correct. You use the ohm setting on your multi meter.

I would personally, go from the contact inside the distributor cap to the plug connector. If you have a bad resistor end- they are replaceable.. IE you don't have to buy a new set of wires. The wires them selves are copper core and silicone insulation.

I would also check the resistance of the dist rotor from center to outside edge. I think they are marked or in the FSM.. I've seen some crazy high readings on them... a little cleaning and it comes down to normal.

Are your insulators behind the distributor caps original?

M

Caps, Rotors and insulators were changed this past Friday....
Spark plugs were put in end of October...

I have a multimeter so I can find the resistance...however, I need to know : Do I take the wires out of the car to check them?? or Do I just unplug the one going into the spark plug and test it from there ( with the other end still attach to the distributor)??

No need to take the wires out. I would start at the plug side by unscrewing the plug boots [admin edit: this works on OE/OEM wires/boots, Bosch/Beru] and measuring the resistance of the boots first (should be around 2K ohm). While the boot is off, you can check the resistance of the wire between the plug end and the distributor but there is no need to remove the wire from the loom. Since these are solid wires, I would expect no resistance there at all.

Also, somewhere on this forum Klink discusses going wider with the gap on new plugs (.1 vs. .08?) because customers had complained that new plugs caused the engine to run rough. Widening the gap to .1 seemed to stop it, as a wider gap causes the spark to jump further and facilitate better combustion.

I would also use some tune-up lube on the boots just to make sure they are making full contact when installed. Sometimes a rough running engine is caused by the boots not being properly seated.

[EDIT]:

No need to take the wires out. I would start at the plug side by unscrewing the plug boots [admin edit: this works on OE/OEM wires/boots, Bosch/Beru] and measuring the resistance of the boots first (should be around 2K ohm).

No worries, Jon! I only mention this as I've seen some aftermarket boots which do not use the M3 threaded connections like the factory wires. Any Bosch/Beru boots should unscrew, but be careful with other brands...

I guess if you measure the plug with the boot, you won't know which is causing the problem, but if you get substantially more than 2K ohm it's probably a safe bet that it's the boot anyway. I think I am one of the few guys on the forum who had a rough idle that was actually attributed to bad plug wires (after changing half the parts on the car to troubleshoot!). The set you made is doing a great job. Thanks.

Track down which wires ard out of spec.. then pull a connector. I've had Beru connectors which did not unscrew properly.
Just sayin, minimize your work. I've got a few spare wires and connectors.. all beru stuff.

FWIW, when I was having idle problems with my 95 E420 a few years ago that turned out to be my plug wires, the wires measured zero resistance and all boots were replaced and within spec. I had replaced and/or checked the stuff on the list below. When I handed this list to the tech at the dealer the day before my appointment and told him that Klink thought it was a secondary ignition problem, he said that he has seen the plug wires short from one wire to the other on these 119's; and since it looked like I had replaced just about every other suspect part, he would suggest that I try replacing plug wires if I had them because that would probably be his first step anyway, presuming his test equipment didn't reveal anythign else. I went home and replaced the wires and it has idled smoothly ever since.

Track down which wires ard out of spec.. then pull a connector. I've had Beru connectors which did not unscrew properly.
Just sayin, minimize your work. I've got a few spare wires and connectors.. all beru stuff.

M

it might seem like a stupid question for you....but HOW exactly do I do that??
Do I use the red or black wire-probe from the multimeter?? and if one goes inside the boot to measure, then where goes the other probe ( from the multimeter )
The only thing that I know how to do with my multimeter is to check my battery ( and therefore if the alternator is charging or not...lol )

You may have to get an extension for your ohm meter like a wire with an alligator clip on each end, so you can span from the plug boot across to the distributor boot. It doesn't matter which side you use the red wire or black wire on, just set your meter to ohms (Kohms if you have it) and stick one probe down into the boot (you may need to clip it to a screwdriver to reach the terminal at the bottom) and touch the other end inside the boot at the distributor. Do you know which plug goes with which terminal at the distributor?

You may have to get an extension for your ohm meter like a wire with an alligator clip on each end, so you can span from the plug boot across to the distributor boot. It doesn't matter which side you use the red wire or black wire on, just set your meter to ohms (Kohms if you have it) and stick one probe down into the boot (you may need to clip it to a screwdriver to reach the terminal at the bottom) and touch the other end inside the boot at the distributor. Do you know which plug goes with which terminal at the distributor?

when the car is cold, the idle will fluctuate a little back and forth ( when in gear, foot on the brake) for example : it will go really fast from 600 rpm to 400rpm back to 700 down to 500...and so on!!)However, it won't stall...after a few seconds, it will settle at about 500rpm....the car only does it when it is cold!!!when the car gets to normal engine temperature, it does not do it anymore...

ANYONE HAS ANY IDEA????? EGR valve?? Neutral safety switch??? any of the coolant temperature sensors??

When the car is warm, this fluctuation does NOT happen....
also, I think that my idle is a little low : about 550-600 in N/P and right ( or just a tiny under) 500 rpm in D/R

I replaced the Caps and rotors on Friday....there is no misfire, and the car runs well on the highway...cruise control works as well.

Harness is from 2005 ( so it is good )
Throttle was inspected and it is also from 2007 ( it is good )
Voltage regulator was replaced ( December)
Crankshaft position sensor replaced
Camshaft position sensor replaced
Fuel pressure regulator replaced ( last week )
Fuel pump working fine ( tested )
I just the spark plugs ( which were replaced in November ) : good.

I will have the NSS installed on Monday at my Indy MB mechanic as I need to go for a brake flush...

I haven't tested the spark plug wires yet....they are bosch, but I don't think they are new ( the PO said that they were replaced, but I don't know when...lol )

As for the codes, I am waiting for my code reader ( from Ebay ) to arrive....

The problem only appears at cold start...so today, I let the engine warm for about 10 minutes before driving, and it was fine...No fluctuation

Replacing the NSS is good preventative maintenance anyway. IIRC, 20 years ago I had a NSS problem on an old 400E where it would idle erratically when shifted into reverse when cold.

Have you checked for any vacuum leaks? I usually use a can of starter fluid and spray it around the engine bay. Try to stay away from directly hitting the injectors. I hear the starter fluid could deteriorate the o-rings. If you hear any RPM change, it could mean a vacuum leak. It should be interesting to see the codes.

Replacing the NSS is good preventative maintenance anyway. IIRC, 20 years ago I had a NSS problem on an old 400E where it would idle erratically when shifted into reverse when cold.

Have you checked for any vacuum leaks? I usually use a can of starter fluid and spray it around the engine bay. Try to stay away from directly hitting the injectors. I hear the starter fluid could deteriorate the o-rings. If you hear any RPM change, it could mean a vacuum leak. It should be interesting to see the codes.

Yep...NO vacuum leaks at all. I did the test and my mechanic ( when the issue started to happen ) also did a smoke test.

Hopefully, the code reader will arrive this week. If not, at least I will know more on Monday, when I have the new ( MB brand ) NSS installed.
Other than that, the car runs super great. acceleration is great at any speed

I just read in the owner manual, that the spark plugs should be F9DC0.
However, I have Bosch F8DC4 right now....So, I wonder if it does make a difference.
Anyways, in doubt I am ordering some F9DC0 from FCP https://www.fcpeuro.com/products/mer...mer-0031596703
They have a lifetime return policy ( when it is time to change the plugs, you send them the old ones, and they send you new ones for free )

I just read in the owner manual, that the spark plugs should be F9DC0.
However, I have Bosch F8DC4 right now....So, I wonder if it does make a difference.
Anyways, in doubt I am ordering some F9DC0 from FCP https://www.fcpeuro.com/products/mer...mer-0031596703
They have a lifetime return policy ( when it is time to change the plugs, you send them the old ones, and they send you new ones for free )

OK...more update: Car rpm does not fluctuate anymore.9 NSS was changes as well as all 3 engine temperature sensors)
Also, there was a S29/3 code, but once the throttle cable was adjusted, the code cleared off...

While the car was plugged in on the computer, I could see that it was reading ( on the computer) a Rpm of 650...however, on the dash it did not look like 650 for me ( or maybe I am wrong thinking that a reading of 650 rpm should be higher on the dash)

Anyways, one of the codes ( mostly the only one actually ) is on the ASR module...

it says :

030 CAN: No reception from EA/CC/ISC/ N4/1

SHould I worry about that???
ASR and cruise control do work, so I am puzzled???

ASR coded 030 frequently appears with NSS codes and other codes. It rarely appears by itself. If this code keeps coming back after you clear it, something is still fishy... and no, you probably do not need a new ASR or E-GAS module.

ASR coded 030 frequently appears with NSS codes and other codes. It rarely appears by itself. If this code keeps coming back after you clear it, something is still fishy... and no, you probably do not need a new ASR or E-GAS module.

Thanks...
Thinking about it, this code reading ( when the 030 appeared ) was done before the NSS was replaced since I can see the s29/3 on the sheet....
I can't recall if it appeared again when the NSS was installed ( since I did not get another printout)...